(1) Field of the Invention
The present invention relates to a process for joining metals, by which a metal having a plated layer consisting of tin or tin alloy is joined to a core wire of a coated electric wire.
(2) Description of the Related Art
For example, a wiring harness arranged in a motor vehicle has wires (electric wires) and terminal metal fittings to be attached to each end of the wires. The wire consists of a core wire made of metal such as copper and an insulating coating for coating the core wire. The terminal metal fittings consists of a matrix of electrically conductive metal and a plated layer of tin or the like, which is formed on the surface of the matrix.
So far, when the terminal metal fittings and the wire are electrically or mechanically joined to each other, a part of the terminal metal fittings has been caulked to a core wire of the wire. Therefore, for example, when the wiring harness is arranged in a motor vehicle, there has been a possibility that the electric connection between the terminal metal fittings and the wire is cut by the vibration of the motor vehicle upon travelling and so on.
The terminal metal fittings and the wire can be electrically or mechanically joined to each other by brazing with using solder. However, in this case, there also has been a possibility that the electric connection between the terminal metal fittings and the wire is cut by the vibration of the motor vehicle upon travelling or by the corrosion of the solder caused by the aging thereof.
It is therefore an objective of the present invention to solve the above problem and to provide a process for joining metals, by which a core wire of a coated electric wire can be securely joined to a metal having a plated layer on the surface thereof.
In order to attain the above objective, the present invention is to provide a process for joining metals, by which a core wire of a coated electric wire is joined to a first metal, on the surface of which a plated layer is formed, comprising:
a first welding step, in which an ultrasonic welding is carried out after placing a part of a core wire of the coated electric wire on the plated layer of the first metal, so that the plated layer is melted, the part of the core wire is joined to a matrix of the first metal, and the part of the core wire is broken off from a body of the coated electric wire; and
a second welding step, in which an ultrasonic welding is carried out after further placing another core wire of the body of the coated electric wire on the part of the core wire joined to the matrix, so that the two core wires are joined to each other.
With the construction described above, the plated layer is once melted in the first welding step. Therefore, when the ultrasonic welding is carried out, the core wire of the coated electric wire and the first metal are pressed in the direction of approaching to each other, resulting in that the part of the core wire of the coated electric wire is securely joined to the matrix of the first metal. The part of the core wire of the coated electric wire is broken off from the body of the coated electric wire.
Thereafter, in the second welding step, an ultrasonic welding is carried out after further placing another core wire of the body of the coated electric wire on the part of the core wire joined to the matrix, the core wire of the body of the coated electric wire can be securely joined to the part of the core wire.
In this specification, the xe2x80x9cbroken offxe2x80x9d means that the core wire of the coated electric wire is cut and the part of the core wire is separated from the body of the coated electric wire. The expression of xe2x80x9cthe two core wires are joined to each otherxe2x80x9d means that the part of the core wire is joined to the another core wire of the body of the coated electric wire.
Preferably, ultrasonic oscillation energy used in the first welding step is higher than that used in the second welding step, and force for pressurization applied in the direction that the core wire and the first metal approach to each other in the first welding step is larger than that in the second welding step.
With the construction described above, by melting the plated layer, the part of the core wire can be securely joined to the matrix of the first metal. Further, when the two core wires are joined to each other, the core wire of the body of the coated electric wire can be prevented from being broken off.